Automatic aircraft propeller synchronizer



April 2, 1952 LA VERNE R. PHILPOTT 2,593,484

AUTOMATIC AIRCRAFT PROPELLER SYNCHRONIZER I Filed NOV. 19, 1945 5Sheets-$heet 1 ILELL grwq/wbom LAVERNE. R. PHILPOTT Gamma April 22, 1952LA VERNE R. PHILPOTT AUTOMATIC AIRCRAFT PROPELLER SYNCHRONIZER 5Sheets-Sheet 2 Filed Nov. 19, 1945 N-N zotbmm Te zoiuwwlv l lmk 295mmLAVERNE R. PHlLPOTT April 22, 1952 LA VERNE R. PHILPOTT 2,593,484

AUTOMATIC AIRCRAFT PROPELLER SYNCHRONIZER Filed Nov. 19, 1945 5Sheets-Sheet 5 gwue/rvm LAVERNE R PHILPOTT LA VERNE R. PHILPOTT2,593,484

AUTOMATIC AIRCRAFT PROPELLER SYNCHRONIZER A ril 22, 1952 '5 Sheets-Sheet4 Filed NOV. 19, 1945 M w M m M n 3 H P R E N R w A .L Ill- EOFOE mmkmszm m h m April 22, 1952 LA VERNE R. PHILPOTT AUTOMATIC AIRCRAFT PROPELLERSYNCHRONIZER Filed Nov. 19, 1945' 5 Sheets-Sheet 5 AUTO NORMAL grwe/wbovLAVERNE R. PHILPOTT Patented Apr. 22, 1952 AUTOMATiC AIRCRAFT PROPELLERSYNCHRONIZER La Verne R. Philpott, Washington, D. 0. ApplicationNovember 19, 1945, Serial No. 629,689 g 4. mains. (or. 170-16017) V(Granted under the act of March 3, 1883, as

The present invention relates in general to amended April 30, 1928;3700. G. 757) of the pitch of the propellers driven by the engines. r

In operation of multi-engine aircraft, one of the problems is tomaintain under normal cruising conditions, the rotational speed of allof the power plants at the same level, to avoid objectionable beateffects set up by lack of synchronization and'likewise toprovideforsubstantially equal power output from all of the power plants.Aircraft engines are now equipped in most instances with controllablepitch "pro 7 pellers, and due to the variable loading effects ofpropeller pitch on the engine as the pitch is varied, recentdevelopments have providedfor automatic control of the propeller pitchas a means of varying the engine speed. 7

One type or controllable pitch propeller is that shown in the BlanchardPatent No. 1,951,320, wherein an electric motor carried by the propellermay be energized to either increase various control circuits andapparatus: elements except those requiring direct mechanical connectionwith the engines to be synchronized are' constructed and arranged to bemounted as a unit directly on the pilots instrument panel of anairplane. T

Another object of the invention'is the provi- 2 staggered section takenon the lines [-1, 22, 3-3, 4-4 of Figure 1;

Figure 3 is a front elevation of a sector of the intermediate mountingplate carrying the es capement mechanisms for controlling the pitch ofthe propellers;

Figure 4 is an enlarged elevation of one of the escapement mechanisms;

Figure 5 is a cross-section of the master motor governor taken on thelines 55 of Figure 2;

Figure 6 is a diagram of a synchronizing system embodying the apparatusshown in Figs. 1 150 5 and the electricalcircuits associated therewith.

Figure 7 is a detail elevation of the support member for the vacuumswitch arm.

Figure 8 is a schematic diagram of the pitch control motor controlswitchboard.

Referring first to Fig.,1, this illustrates the front view of thecontrol unit as it appears on the pilots instrument panel and consistsof a conventional drag-cup tachometer indicator I0 or decrease the pitchof the propeller; blades? sion of a synchronizing'system in. which thevarious control circuits and electrical contacts are constructed andarranged to be mounted'in -a single enclosed unit adapted to bepressurized so as to remove any effects high altitude may have on theelectrical "characteristics of the system. Other objects, advantages andcapabilities of the invention will become apparent from the trol unit;

Figure 2 is a composite vertical, longitudinal trols necessary forefiective operation of the synchronizing system. The knobs H and i2 areprovided with disks integral therewith adapted to be selectively held byany conventional clamping members, such as those shown in Fig. 2, tohold the control knobs in their position of adjustment against shiftingdue to vibrations in the aircraft.

Referring now to Fig. 2, there is shown a housing [3 completelyenclosing with rear and front plates [4 and 33 the various controlcircuits and apparatus elements of the system, and adapted to bepressurized to prevent any variation of the pressure surrounding theelectrical contacts and control devices, to be later described, due tovariation in the altitude at which the system is operated. Theelectrical outlets and bearings for control knobs, etc. wouldaccordingly be provided with seals or packing to prevent leakagetherefrom. In addition, a conventional motor-driven pump may be coupledto the shaft of the master motor and controlled by a valve mechanism inthe pressurized housend bya bearing member 21.

in intermediate mounting bracket 32.

shaft l8.

ing for pumping air into the housing and maintaining the pressure at apreset level. This is to reduce the tendencies of the contacts to burnseriously when the pressure surrounding the contacts is low and thus toincrease the life of the contacts which, in the absence of such anarrangement, can completely burn out in less than one flight. Mounted onthe mounting plate Ma supported within this housing are a master motor15, a timing motor [6 and a plurality of three phase synchronous motors,such as motor l1, each of the synchronous motors being electricallycoupled to the field output of a three phase generator, such as thegenerator I 53'shown in Figure 6, the rotor of which is mechanicallycoupled to the output shaft of one of the engines.

In Figure 2 and the following description, only one of these synchronousmotors and its associated circuits are shown or described, since thesynchronizing circuits. for each of the motors operate in conjunctionwith the master motor IS in the same manner. Figure .3, however, showsthe escapement mechanisms for each of the engines of a two-engineairplane mounted in proper relation with the timing shaft.

Synchronizing of the engines is accomplished, generally, by setting thespeed of the master motor l to a desired value, and comparing the outputof the master motor [5 with that ofeach of the three phase synchronousmotors individually, each of which duplicates the output of pled to theoutput shaft [8 of the above mentioned timing motor [6 is a governormechanism comprising a spacer sleeve [9 keyed to the shaft l8 andcarrying centrifugal governor weights 2D and 2| by means of ,pivotallymounted arms 22 and 23. A sliding drum 24 is slidablymounted on shaft I8and carries a ring-like shoulder 25 positioned to engage the arms 22,23' of theigovernor. Engaging the opposite surface .of the drum 24 is aresilient spring member .26 surrounding the shaft 18 and abutted at itsother Surrounding the bearing member 2! is a threaded sleeve 28 keyed toa control shaft 29 and supporting .by athreaded connection a frictiondrum 3!]. The threaded sleeve 28 is supported by a bearing 3! mountedThe control shaft 29 extends through the front plate 33 of the housingl3 and is keyed to the timing motor control knob 12. Itshould beapparent thatrotation of the control knob l2 will rotate the threadedsleeve '28 within its bearing 3|, thereby shifting the friction drum 30,threaded to the sleeve 28, toward or away from the'sliding drum 24. Asthe speed of rotation of the timing motor shaft [8 is increased fromzero, the centrifugal force on the governor weightsxZil, 2!

increases, extending the governor arms 22, 23

to a positionmore nearly perpendicular to the This increasing speed, byincreasing the angle between the governor arms and the shaft, shifts thesliding drum 24 bearing against longitudinally within bearing 59.

the arms 22, 23 toward the stationary friction drum 30 until the speedis such that the sliding drum 24 is prevented from sliding by engagementwith the friction drum 30, thus determining the maximum speed of themotor since the governor mechanism applies a braking action at thisspeed to load the motor down.

The timing motor 16 drives a timing gear 46 in an escapement mechanismI48 controlling the propeller pitch control motor through a helical geartrain comprising gear 34 mounted on shaft l8, gear 35 meshing therewith,shaft 36, gears 37 and 38, shaft 39, gears 46 and 4|, shaft 42, gear 43on shaft 42, gear 44 mounted on shaft 45 and timing gear 46 meshing withgear 44.

The above mentioned mechanism for controlling the speed of the mastermotor and comparing it with the speed of each of the engines is asfollows. Referring still to Fig. 2, keyed to the shaft-41 of mastermotor i5 is a governor housingsleeve 48, shown in cross section in Fig.5, having a hollow cylindrical portion through which-extends atransverse shaft 49 mounted at oppositesides of the housing to form apivot for the governor arms 50, 5|. The governor arms 50, 5| extendthrough slots 52, 53 in the governor housing sleeve 48. Aslot 54 is cutinto the governor arm at a point away from that at which the arms 50, 5|are pivoted to hub 49 and extending parallel to the longitudinal axis ofthe arm 50. Mounted on the outer or free end of the arms 50, 5| areweights 55, '56 one extending forward of the arm on which it is mountedand the other extending aft of its arm, so that as the speed of rotationof the governor housing sleeve 48 is increased, the centrifugal force onthese weights 55, 56 due to the rotation of the arms 50, 5| orientatesthe arms away from the perpendicular to the shaft 41. Supported withinthe housing sleeve 48 and abutting against the governor arms 50, BI is apush-rod head 5! having a shaft extension 58 of reduced diametersupported within bearing rollers 59 and the ball thrust bearing in theblock 62 and free to slide Gear hub- 68 is bored out to clear the shaftextension 58. Mounted ata point on the circumference'of the push-rodhead 51 and extending parallel to the axis of shaft 41 into the slot 54of governor arm 50 is a pin -:6l. The complete governormechanism ishoused in a surrounding thick-walled cylinder 48a enclosing the arms 50,5| and supported atboth ends we supporting disk, one bearing on each endof the housing sleeve 48. This provides-the motor with a sufficientlylarge moment of inertia or fly wheel effect to maintain stable or onlyvery slightly erratic speed regulating irregularities about the desiredoperating speed. If the housing cylinder and thus the moment ofinertiais too small, large amplitude speedhunting will result. Abutting thefree end of the shaft extension 53 is a block member 62 carrying thepivoted arm 63 of a conventional vacuum switch 64 which controls thespeed of master motor l5 by means of a pair of normally closed contactsconnected across a resistor in series with'the windings of motor l-5.The pivoted arm 63 issurrounded by a damping material such as rubber inthe block 62 to prevent contact chatterin the switch 64. The blockmember 62,

shown in detail in Figure 7, has downwardly extending members 10!, 102connected thereto, .extending parallel to the pivoted arm 63 past themain body of switch 64. The members 10!, 102

move parallel only to the axis of shaft "I0.

5 are provided with a counterweight I03 on their lower extremitiessurrounding the glass envelope of the vacuum switch 64 and are pivotedon pins I04, I05 to the intermediate mounting plate 32 near the point ofentry of the arm 63 into the body of switch 64 to properly regulate themovement of block 62. A threaded member I06 having a knurled knob it?extending therefrom is likewise provided to lock the position of switch64 in seating bracket 160 mounted to move in a direction perpendicularto plate 32. A wedge shaped member I09 is adjustably positioned toengage an inclined face of the seating bracket 108 and controlled by anadjusting rod H threaded into the wedge member I09 for varying theposition of the seating bracket I08 and thus the switch 65 with respectto the intermediate mounting plate 32. Resiliently urged against theopposite side of the block member 62 is a lever 65 pivoted on a yoke 66.The other end of the lever 55 is connected by means of a spiral spring67 to a stud 68 on slide member 69 surrounding the shaft 70 keyed to amaster motor control knob I I, the shaft having threaded portions II and18. The end of spring 61 adjacent the lever 65 is secured to the lever65 by means of a turnbuckle stud by which the tension of the spring andthus the maximum speed permitted by the governor mechanism may beadjusted during assembly. The shaft I0 is supported within a fixedbearing housing I2 having a longitudinal slot I3. The housing l2 alsosupports the slide member 69 threaded on its inner surface at '50, thethreads '74 being positioned to engage threaded portion ll of shaft 10.The slide member 65 also carries a stud member I extending into thelongitudinal slot 13 in the housing'IZ to allow the slide 69 to A fixedbearing nut i6 is mounted within housing 12 and is threaded at I? toengage the threads I8 on shaft l0. Threads I? and T8 are pitched in theopposite direction as threads 'II and 74 so that a given degree ofrotation of knob II will move the sleeve 69 through twice thelongitudinal distance that a single pitch threaded drive would move thesleeve.

Thus, rotation of knob II rotates and axially shifts the shaft 70,driving the slide member 69 through threads II and 14 toward or awayfrom the lever 65 and increasing or decreasing the tension on theconnecting spring 61, since the slide 69 is prevented from rotating bystud I5 and slot I3.

Assuming the direction of movement of the slide 69 is away from lever65, the force in the direction of the block member 52 and thus on switchplunger 33 will be increased. Thus, a greater speed will be required ofthe master motor I5 to so orientate the governor arms 50 and 5| awayfrom the perpendicular to the axis of shaft 41 that the push-rod head 51and extension 58 are cammed against the bar member 62 with sufficientforce to overcome that of the lever 65 and move the block member 62 andplunger 63 to open the contacts in vacuum switch 64, The motor speedingup to the predetermined speed to whichthe governor is set maintains arepeated opening and closing of the switch 64 in response to slightincrease and decrease in speed with respect to the chosen standard. Eachopening of the switch upon increased speed opens the shunt circuit toinclude a resistor in series in the motor circuit which effects areduction in motor speed to just below the standard with maintained atsubstantially constant speed, the

variation in speed being so small in degree and their duration'so briefas to be negligible. The slot 54 and pin BI are employed to increase thesensitivity of the governor control, since the component of movement ofthe governor arms at any given point away from their pivotal point inthe direction of the axis of shaft 4? as the governor arms areorientated in that plane is greater at the center of the arm than at oneof its edges, i. e. the slippage which a rider cam would experience in adirection perpendicular to the axis of shaft 41 would be far greater ifthe cam were engaging an edge of the governor arm.

The means for coupling the output of master motor I5 to a subtractingdifferential gear system I9 by which it is compared with the output ofone of the three phase synchronous motors I1, and thus of one of theengines, is a speed reduction gear train comprising helical gear mountedon the governor housing 48a to rotate therewith and driving through gear8| a helical gear 82 on hub 83 of gear 84. Gear 33 of the differentialI9 thus provides the input from the master motor I5. The output from thethree phase motor I1 is coupled to the gear 85 or" the differential 19by means of gear 80 keyed to the output shaft 81 of motor I1 and gear 86meshing with gear 86 and mounted on the hub 85 common to both gears 88and 85. The subtracting output of these two input speeds is coupled fromthe differential I9 by shaft 96 directly to trip rotor 9| in theescapement mechanism I658 controlling the propeller pitch-control motor.Thus any difference in the speeds of the engine and the master motorwill result in rotation of the trip rotor 9I in a direction determinedby the greater of the two speeds.

Referring now to Figures 2, 3, and 4 the escapement mechanism I48controlling the propeller pitch-control motor, one of which is providedfor each engine, is as follows. Mounted coaxially with the abovementioned timing gear as on a shaft 92 are a pair of ratchet wheels 93and 94, one on each side of gear 45. These ratchet wheels 93 and 94 arefree to rotate with respect to shaft 92 and are adapted to be drivenindependently and frictionally by gear 58 through friction clutch disks95 and 96 axially slidable on the shaft 92 and holding the ratchetwheels 93 and 94 between the clutch disks 9%": and 96 and clutch disks9'! and loosely mounted on shaft 92. The clutch disks and 96 are urgedresiliently against the adjacent faces of the ratchet wheels 93 and 94by springs surrounding the shaft 92 and heldbetween a face of the clutchdisks and an adjustable shoulder member on shaft 92, the pressure of theclutch springs being adjustable by positioning the shoulder member bymeans of lock nuts on the ends of shaft 92. Engaging a shoulder ofratchet wheels 93 and 94 in normal position are pawl members 99 and I00,pawl 99 abutting a shoulder on ratchet wheel 93 and pawl I00 abutting ashoulder on ratchet Wheel 94. Pivoted to the lower portion of pawls 99and I00 at points I0l, I82 is a connecting lever I03 having shoulderextension portions laidand I05, one at each end of the lever lt-B,adapted to engage stop pins I36 and Ifll, respectively, on intermediatemounting plate I58, the pins I06 and I 01 defining the limit ofcounterclockwise rotation about its center of which the lever I03 iscapable. Also connected to the ends of lever I03 are spring members I09and H0, each secured at their other end to the mounting plate I08 so asto urge the lever I03 to rotate away from the stop pinsgI06, I97.Pivotally connected by a pin III to the center of the connecting leverI93 is a main arm H2 pivoted on its ,center by a pin H3 on the mountingplate I98 and carrying on the end opposite that connected to lever I93two electrical contact members H4 and H5. The main arm H2 is atelectricalground by virtue of its flexible electrical connection (notshown) to plate I98. Positioned to be engaged by contact members H4 andH5 respectively, when the main arm H2 is rotated about pin I I3, arecontacts I I5 and I I1, mounted on contact arms H3 and H9, respectively,the contact arms H8 and H9 being pivotally mounted on plate I08 by pinsI20, I2I and resiliently urged toward the contact members H4 and H5 onmain arm H2 by spring members I22 and I23.

The. contacts H4, H5, H5 and II! are in the field winding circuit of anelectric propeller pitch motor having increase and decrease field coils,one for operating the motor in a direction to increase the propellerpitch and the other in ,a direction to decrease pitch, the contacts H4,H5 energizing the motor to rotate in such a direction as to increase thepitch of the propeller when the contacts are closed, while contacts H5,H1 energize the motor to rotate in the direction to decrease the pitchof the propeller. This is accomplished by virtue of the fact that thecontacts H5 and II! close the circuit to opposite field coils in themotor, comprising an increase coil arranged to run the motor in adirection opposite to that caused by the decrease coil. To determine theposition contacts H6 and I I? occupy in normal condition with respect tocontacts H4, H5, insulating blocks I24 and I25 are mounted on the freeends of contact arms H9 and H9, respectively, and extend outwardlytherefrom to engage stop members I28 and I2? adjustably positioned onadjusting member I28 on mounting plate I08. Also connected between theabove mentioned pawl members 99, I99 is a spring I29 resiliently urgingthe teeth of the pawl members 99, I90 toward each other and thus towardthe ratchet wheels 93, 94.

Pivoted to the upper portion of the pawl members 99, I50 are triggersI39 and I3I, and positioned so that the endof one of the triggers I35and I3! will be engaged by one of the lugs I32 on trip rotor 9| when thetrip rotor is rotated. Urging the trigger I39 downwardly against a stopI33 on the pawl 99 is a spring I 34, the stop I33 carrying the end oftrigger $30 upward out of position to engage the lugs I32 when the pawl99 is moved upward. A spring I35 is arranged to urge the trigger I3Idownward against a stop I35 on the mounting plate I99, the stop I35camming the trigger I3I upward out of position to engage the lugs I32when the pawl I is moved downward.

Operation ofthis escapement mechanism is as follows. Assuming acondition of normal operation in which the speed of the master motor Iand the three phase synchronous motor I1, and thus the engine, are thesame, the output of the subtracting differential is zero and the triprotor 9! remains stationary. The timing gear however, is continuouslyrotated, due to the constant speed drive of motor I9 and its gear train.The condition of the escapement mechanism is as shown in Fig. 4 in whicha shoulder of the ratchet wheels 93 and .94 is in engagement with oneend of pawl 99 and pawl I00, respectively, urging the pawl 99 downwardand pawl I00 upward to a position whereby the shoulders I94 and I05 ofthe lever I03 connected between the pawls 99, I00 engagestops I06 andI07. Thus, the gear 46 and its associated friction disks 95, 96, 9? and98 may be rotated continuously but no motion is transmitted to theratchet wheels 93, 94 since they are held against rotation by the pawls.This condition centers arm H2 and maintains contacts H4, H5 and H5, H1in an open condition.

However, if the speed of the engine decreases to a value below that ofthe master motor I5, the differential I9 yields an output proportionalto this difference in speed and in the same direction as gear 84 whichis driven by the master motor. This difierential output drives the triprotor 9i in the escapement mechanism in, for example, a counterclockwisedirection, bringing one of the lugs I32 in to engagement with triggerI39 and forcing the trigger I30 and the pawl 99 connected thereto awayfrom the trip rotor ill and moving the end of pawl 99 out of engagementwith the shoulders on ratchet wheel 93. The pawl I09 is not disturbed,since rotation of the trip rotor 9i in a counterclockwise directionmerely cams the trigger I3I upward against its spring I39, thus allowingthe pawl I09 to be held against downward movement. With the pawl 99 outof engagement with the ratchet wheel 93, the spring I09 carries pawl upand over the shoulder of ratchet wheel 93, thus carrying the ends ofconnecting lever I03 connected thereto upward and rotating the lever I03about the stop Iil'I. This rotation of lever I93 lifts the end of themain arm I I2 pivoted at I I I to the center of lever I03, therebyrotating the main arm H2 clockwise about its center pivot H3 to engagethe grounded contact H5 on the main arm H2 with the lower contact H1,closing the circuit to the decrease field coil of the propellerpitch-control motor to decrease the pitch of the propeller and therebydecrease the loading on the engine. The disengagement of the end of pawl99 with ratchet wheel 93 allows the ratchet wheel to be rotated with thetiming gear 43 through friction disks 95 and 91. Pawl 99 simultaneouslyflies upward till it disengages trigger I30 from lug I32 at which timespring I29 returns the face of pawl 99 against the face of ratchet 93.It continues upward till it strikes the next shoulder of ratchet wheel93. At about half way up in its stroke (pawl 99) contacts H5 and H1 areclosed. The remainder of the stroke of 99 causes a rotation of contactarm H9 against the spring I23. As ratchet wheel 93 continues to turn,pawl 99 is gradually returned to its downward position, opening contactsH5 and II! on its way and finally seating in its former position asdetermined bythe stop I96, thus completing one correction cycle. Thecontact arms H3 and H9 are pivotally mounted to enable the contact armto be carried downward or upward with the contact-II4 or H5 when inengagement therewith when the main arm I I2 is rotated, thereby allowingthe contacts to be closed for a fixed maximum period of time during eachcorrection cycle. The duration of this period is determined by thesetting of the adjustable stops I26 and I21, and the speed of the timingmotor driving ratchet 93. It will be apparent that the setting of thesestops I26, I27 and the speed of the timing motor I3 thus determine thetime the propeller pitch-control motor is energized, and thus the changein propeller pitch, during each correction cycle.

If the engine and thus the motor I'I were rotating at a speed greaterthan that of the master motor I5, the differential output would rotatein the opposite direction, rotating the trip rotor 9I clockwise andtripping pawl I to close the upper set of contacts H4, H6 and.

of Figures 1 to 5 with ancillary circuits and apparatus connected forsynchronizing two airplane engines I31 and I38 provided with adjustablepitch propellers I39 and I40 through which adjustment of the enginespeed, over a range ample for synchronization, is effected by adjustmentof the propeller pitch. Such adjustment is accomplished through aconventional reversible pitch control motor, such as motor I4Iassociated with the engine I31, having increase and decrease field coilsI42 and I43, one for operating the motor in a direction to increase thepropeller pitch and the other in a direction to decrease the pitch. Oneend of each of the coils is connected through conductor I44 to thepositive end of the ships battery I45, the negative end of the batterybeing connected to a common or ground connection including the metal Iframe of the machine. The other end of the increase and decrease coilsare connected through conductors I46 and I4! to the contacts H6 and H1,respectively, in the above mentioned escapement mechanism I48 through acontrol switchboard I49. The contacts H4 and II 5 on main arm I I2 arepositioned to engage the contact H6 or H1 when the arm is pivoted by theescapement mechanism connected thereto in re-' sponse to a rotationaloutput from the differential 19 to ground the end of the increase ordecrease coil through contact H6 or III, completing the energizingcircuit to the coil to drive the propeller pitch-control motor in thedirection determined by which of the field coils is energized. Similarlya pitch-control motor I50 for varying the pitch of propeller I in engineI38 is operatively connected to an escapement mechanism I5I similar tothe escapement mechanism I I48, the mechanism I5I being responsive tothe output of differential I52 comparing the speed of the master motorI5 with that of engine I38. Each engine is also provided with a threephase generator, such as units I53, I54, the rotors of which are coupledto the propeller shafts of propellers I39, I40, respectively, fordriving their associated synchronous motors I1 and I55 in thesynchronizing device at a constant ratio to the speed of the engine.

The control switchboard I49, shown in detail in Figure 8, is provided toturn on and 01f the synchronizer as a unit, and which will enable thepilot to throw the propeller pitch control of each engine separately, orall of them collectively,

into either automatic or manual operation. Referring to Figure 8, theleads I41, I46 from they decrease and increase coils, respectively, ofthe" contact of the feathering limit switch 804.,

The movable arms of limit switches -80-I, 8 02 and is gconnected acrossthese. contacts inshunt there:

'witl1,,: hikewisega capacitor I51 in seriesiwith a- 10 804 areconnected to the movable arms 805, 806 and 801, respectively, these armsbeing ganged together to form a normal-feather switch 808.

These arms are adapted to be moved in unison ,and engage one of two setsof contacts, one set connecting the leads from the decrease and increaselimit switches Bill, 802 through an automanual switch 809 to thecontacts H1, H6 and open the circuit from the feather limit switch 804,and the other set opening the leads from the limit switches SM, 302, andgrounding the lead through the feather limit switch 804. 'Theauto-manual switch 809 comprises a pair of movable contact arms 8I0, 8Hconnected to the decrease and increase coils I43, I42, respectively,through switch 808 and adapted to engage selectively a pair of contactsconnected to the contacts H1, H6 in the escapement mechanism forautomatic operation or a set of contacts connected to contacts 8I2, 8I3respectively in manual pitch control switch 8I4. This switch 8I4comprises the decrease and increase fixed contacts 8I2, 8I3 and apivoted contact lever 8I5, electrically grounded, and associated with apair of springs 8I6, 8I'I adapted to return the lever 8I5 to centerposition when manual pressure is,

released from the lever. Thus three switch handles are provided for eachmotor, the normalfeather switch 808, the auto-manual switch 809, and themanual pitch control switch 8I4. A main on-off" switch, not shown, isalso provided in the supply circuit to the master motor I5. Themechanical motion involved in turning the on-off switch to "off positionmay be interlocked with the auto-manual switch 809 in such a way as tounlatch the auto-manual switch for each engine to insure that'thepropeller pitch motor control is never left in automatic position whenthe synchronizer is not operating. The switches may be furtherinterlocked so that each switch can be thrown independently; from Manualto Auto and back when the synchronizer is energized and operating. Thus,if trouble were to develop suddenly anywhere in the system so that anyone of the engines begins to change its speed from that at which it wasnormally operating, the pilot could turn off the main switch,deenergizing the unit and throwing all, the engines on manual control.As the pilot locates the trouble, he can then throw the engines backonto automatic operation independently after turning the main on-off"switch to on leaving the offending engine to be nursed by hand. Thefeather limit switch 804 is provided to allow the blades of thepropellers to be feathered or put into a neutral position in case anengine fails completely and must be stopped. The electric brake 8I8controlled by solenoid M9 is provided for each pitch control motor, andis adapted to be actuated by current passing through the armature leadof motor I4I to lock the propeller pitch against changing when the motorI is not energized. This brake'is spring engaged and electricallyreleased.

' Shown at the left of Figure 6 is the electricalv circuit formaintaining the speed of the master motor I5 at the preselected valueand indicating when the motor is operating at this speed. The normallyclosed contacts of the vacuum switch 64 are placed between one of thefield coils of the master motor I5 and ground, thus in series in theenergizing circuit of the motor. A'resistor I56 low resistance pilotlampI58 is connected across themotor control resistance I56 andconsequently:

in shunt of'thecontacts of vacuum switch 64 as an" arcsuppressionifilter and indicator Thus the instantaneous surges of .currentoccurring.

when .the contacts open or closewill illuminate the. pilot lampsubstantially continuously when This lampv is positioned behindatransparenti window in the front panel33. of: the housing unit to bereadily the: master motor is on speed.

have. been adjusted for the proper amount. of:

change. of pitch of the propeller duringone correction'cycle of thesystem, i. e. the time duration offiow of current. through the contacts;if the speeds of rotation of the master motor [5 and'of the enginecoupled to one of the subtractingdifferentials 19, I52 are. difierent,rotational output will be producedfrom the differential the direction ofwhich is determinedby which of thetwo speeds under comparison isgreater. This output, coupled to. the trip rotor 91 in theescopementmechanism controlling the propeller pitchcontrol-motor for the engine towhich. the differential is coupled, trips one of the pawls 99, I00,for'examplepawl 99, out of engagement with the shoulders on-the ratchetwheel 93 which it engaged and allows the ratchet Wheel to be rotated bythe driving force of atiming gear. 16 through friction-disks 95 and 91.Likewise, tripping the pawl 99 allows it to be drawn upward by thespring I09" connected between the pawl and the mounting plate I08, thusrotating the lever I03 and the main arm H2 coupled thereto to close thecontacts N5, I IT to one field coil of the propeller'pitch control motorand vary the pitchof the propeller. These contacts are, of course,re-opened a short time before the next succeeding shoulder on theratchet wheel 93 has driven the pawl 99 against the force of spring W9back into its initial position. These correction cycles are continued,due to the error signal output of the difierential, until the mastermotor and the en- .gine are accurately synchronized and the trip rotorno longer rotates. This variation of the pitch of the propeller variesthe loading on the engine and thus the engine speed, i. 0. increasevarythe engine speed accordingly. Thus, the amount of change in pitchapplied during each 7 cycle can be adjusted to prevent over correctionand consequent hunting without materially reducing the overall responsetime of the system.

This effectively amounts to applying a small pitch correction and thencomparing the engine output witha given standard to determine if thecor-= rection has produced the desired change, then in the appendedclaims.

repeating this-cycle until the engine operates in proper relation with;the. standard. 7

Another desirable feature of this system is that, due to the fact thatthe speed of rotation of the difierential output and thus of the triprotor. is directly proportional to the magnitude of the differenceinthe. speeds of the engine and the'master motor, i. e. the amount theengine is outoi'synchronism, for large error outputs from thedifferential the correction applied to the propeller is very large,while the correction becomes; very small when only small magnitudeerrorjsignals. occur. This produces a substantially instantaneouscorrection of the engine speed; to near synchronization when the enginefallsfartout' of synchronization, such as when one side of the planeenters an air pocket. For example, this. system was found to correct fora speed-difference of 600 R. P. M. in approxi- ,lnately 41.58C0lldSftObring the engine to within 10 R. P. 'M...of synchronization, andrequired an additional 4 to 5. seconds to lock the engine intoexactisynchronization.

Thisirapidcorrection of large errors occurs by virtue. oflthefact thatthe trip rotor 53! is driven at'a rapid speed, thereby retripping thepawls beforethey have been driven far enough toward the seating positionto open the contacts l l4! [5 or ll5--|ll,.dueto contact arms H8 and H9being-able tofollow the contacts H4 or H5 part way home. This causes thecontacts on the main armito belclosed continuously until the trip rotorbegins to'slowdown, thus applying a continuous correction instead of asmall, intermittent one. The relationship: of timing motor speed andrelated i contact adjustments can be regulated to maintain continuouslyclosed contacts when the difierencespeed of any engine to standard isgreater:than about 10 R. P. M.

Various modifications may be made in the invention withoutdeparting fromthe spirit and scope thereof, and it is desired therefore that onlysuchlimitations shall be placed thereon as are imposed by the prior art andare set forth The invention described herein may be manufactured andused by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereonortherefor.

What is claimed is:

1; In an engine synchronizing system, a master motor, a controlledengine, a variable pitch propeller driven by said controlled engine,reversible pitch-adjusting means for said propeller, a pair'of controlcircuits for said pitch adjusting means; one for effecting an increaseand the other a decrease in pitch, subtracting differential. meanscoupled to said motor and said engine, a pivoted contact member commonto either of said control circuits and positioned to selectivelyenergize one of said circuits, an escapement mechanism controlling theposition of said contact member comprising a pair of pawl memberscoupled to said contact member, means 'normally holding said pawlsagainst operation whereby neither of said control circuits areenergized, and tripping means for said pawls coupled to the output ofsaid differential means for actuation in response to a difference in thespeeds of said motor and said engine to trip one or the other of saidpawls and permit said contactmember to energize one or the other ofcontrolcircults. I

2.- In' -an engine synchronizing system, a master motor, a controlledengine, a variable pitch propeller driven by said engine, reversiblepitch-adlusting means for said propeller, a pair of control circuits forthe pitch-adjusting means, one for eifecting an increase and the other adecrease in pitch, a subtracting differential gear system coupled tosaid master motor and said controlled motor, a pivoted contact membercommon to either of said control circuits and positioned to selectivelyenergize one of said circuits, and an escapement mechanism controllingthe position of said contact member comprising pawl members coupledtosaid contact member, holding means normally positioning said pawlmemberswhereby neither of said control circuits are energized, spring meansurging said pawl members and said contact member into a position wherebyone or the other of said control circuits is energized, and trippingmeans coupled to the output of said differential and actuated by adifierence in the speeds of said motor and engine to disengage one ofsaid pawl members from said holding means whereby said spring means mayshift said contact member to energize one of said control circuits.

3. In an engine synchronizing system, a master motor, a controlledengine, a variable pitch propeller driven by said engine, reversiblepitchadjusting means for said propeller, a pair of control circuits forthe pitch-adjusting means, one for efiecting an increase and the other adecrease in pitch, a subtracting differential gear system coupled tosaid master motor and said controlled motor, a pivoted contact membercommon to either of said control circuits and positioned to selectivelyenergize one of said circuits, an escapement controlling the position ofsaid contact member comprising a pair of pawl members coupled to saidcontact member, spring means urging said pawl members and said contactmembers into a position whereby one or the other of said controlcircuits is energized, a pair of ratchet wheels having shouldersabutting said pawls, said ratchet wheels being frictionably driven tohold said pawls and thus said contact member in a position wherebyneither of said circuits is energized, and tripping means coupled to theoutput of said difierential means so as to be actuated when a differencein the speeds of said motors occurs to disengage one of said pawls fromthe ratchet wheel associated therewith, thereby allowing said springmeans to position said pawls and said contact member to energize one ofsaid control circuits.

4 In an engine synchronizing system, a mas- 55 adjusting means for saidpropeller comprising a motor having two field coils for driving saidmotor in opposite directions, said motor being coupled to said propellerso as to increase the propeller pitch when rotating in one direction andto decrease the pitch when rotated in the opposite direction, asubtracting differential gear system coupled to said master motor andsaid controlled engine, a pivoted contact member positioned toselectively energize one or the other of said field coils, and anescapement mechanism controlling the position of said contact membercomprising a lever pivoted at its center to an end of said contactmember and at each end to a pawl member, stop means engaging each end ofsaid lever and defining its normal position in which neither of saidfield coils is energized, spring means urging said lever to rotate aboutone or the other of said stop means, ratchet wheels being frictionallydriven to hold said pawls and thus said lever in their normal positionagainst the force of said spring means, and tripping means coupled tothe output of said differential and actuated by a difference in thespeeds of said motors to disengage one of said pawls from the ratchetwheel as sociated therewith thereby allowing said spring means to rotatesaid lever about one of said stops and position said contact member toenergize one of said field coils, said frictionally driven ratchet wheeloperating, when said pawl is disengaged therefrom, to bring a succeedingshoulder into engagement with said pawl and return said pawl to itsnormal position after a given interval of time.

LA VERNE R. PHILPOTT.

REFERENCES CITED The following references are or record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,076,202 Lewellen et a1. Apr. 6,1937 2,160,324 Berges May 30, 1939 2,251,388 Bates Aug. 5, 19412,261,145 Dickey Nov. 4, 1941 2,271,629 Couch Feb. 3, 1942 2,314,610 DayMar. 23, 1943 2,322,114 Clare et a1 June 15, 1943 2,399,685 McCoy May 7,1946 2,431,687 Drake Dec. 2, 1947 FOREIGN PATENTS Number Country Date517,117 Great Britain Jan. 22, 1940 671,248 France Aug. 31, 1929

